Production of low-carbon iron-chromium alloys



latented Aug. 24, 1926.

UNITED STATES PATENT orries.

B'YnAMJr n. SAKLATWALLA, or GRAFTON, rENNsYLvANIL PRODUCTION OFLOW-OARBOH IROH -OHROMIUM ALLOYS.

' No Drawing.

The present invention relates to the pro duction of low-carbon iron-chromium. 'aI- loys and has for its object the production of low-carbon. iron-chromium alloys directly from the chrome .ore. and at lower tempera- I tures than those heretofore employed. The

invention is particularly applicable to the production of low-carbon .ferro-chromium and will be described'with particular reference to it, it, being understood however that the invention is applicable to other lowcarbon iron-chromium alloys, such for example as chrome steels or irons.

In the manufacture of ferro-chr omium, the most commonly used ore is chromite, in which the chromium occurs as the sesquioxide Cr O incombination with iron inthe form of ferrous oXide-FeO. As invarable constituents of chromite, besides theCr O and F eO cpntents, there are always present certain percentages of alumina (Al O and magnesia (MgO) which render the chromium content very refractory-to ordinary processes of reduction.

The reduction of the chromium content by means of carbon and separation of metal,

from the gangue can be effected at comparatively high temperature, when the oxygen, originally combined with the chromium, is

removed only to be more or less replaced by the element carbon." The result of such a reduction is, therefore, a low grade product, containing approximately eight to four pervcent carbon, depending upon the amount of carbon used, in theoretically calculated pro-- portion or less, the yield naturally being lower with the lower carbon percentage.

The reduction of chromite by means of metallic reducing agents, such, for example, as silicon, is carried out, atthe present time, only m an electric furnace, at high temperature, under expenditure of considerable electricalenergy; as, in spite of. the exothermicity of the reduction reaction, con-- siderable extraneous heat is required to be added, to enable the refractory COHSt-ItHQHtS falumina and magnesia, present in the ore,

to form into a'liquid slag, allowing through separation -of the metal in regulin form. A

further disadvantage of this necessity of using an electric furnace for the carrying out of the process is the opportunity; afforded to the reducing mixture of coming in contact with and picking up carbon from the electrodes, thus lowering the quality-of the metal' produced. For this reason, it has Application filed March 11, 1922. Serial No. 548,083.

been, up to now, necessary, for the production of low-carbon ferro-chromium, to re sort to the expediency 'of refining-a higher carbon content alloy. This refining is accomplished by oxidizing the carbon content .by gaseous, solid, or molten oxidizing agents.

During such a process, however, a certain percentage of the chromium is oxidized simultaneously with the carbon and is lost, rendering the operation very uneconomical.

In accordance with my. method, the above deficiencies. are obviated, and the chromite is reduced to low-carbon .ferro-chromium with a complete regulin separation of the metal by means of temperatures which are attainable Ifa reverberatory or crucible furnace.

the

combustion-heated furnace is used,

higher cost of electric furnace operation may be eliminated, as well as the disadvantage of the absorption of carbon -,into the metal from the electric furnace electrodes. If an electric furnace is used, the process may be carried out at a lower temperature in the ordinary combustionheated furnace, such as a gas orcoke-fired.

than that hitherto employed, with 'consetory constitutents of the chromite and form a slag which is fluid at the lower reduction temperatures, such as are a titainable in a combustion-heated furnace. he flux preferably contains a material, such as a; fluoride, which will produce a slag whichis liquid at the desired temperaure. The added fluxing materials combine exothermically with the silica produced by the oxidation of the silicon and with'the refractory constituents .of the ore, and thus augment the tempera tureproduced by the reduction reaction.

Furthermore," the compounds caused by the combining with the flexing material and the silica and refractory constituents of the ore have a low melting'point and a low specific heat.

The fluxing material having the above indicated desirable qualities may be form'ed of a mixture of about equal amounts of lime and fluorspar. The mixture of lime and fluorspar is'added to thereduction mixture manganese,- aluminum,

which consists of chromite with silicon in theoretical proportions necessary for the reduction of its Cr O and FeO contents.

The amount of lime (0210) to produce the desired result has been found to be between and 7 0%- by weight of the silicon (Si) beneficial to the reaction has been found to'.

be, inamount, about equal to that ofthe lime or in a slight excess of the lime.- Other metallic oxides, such as ferric-oxide and manganese dioxide, may be used and pro-.

duced by exothermic reactions similar lowmelting compounds in the presence of fluorspar. Such other metallic oxides may ,re place in molecular proportions a part of the lime in the lime fluorspar mix. The addition ofboron trioxide up to about 5% of the lime accelerates the reaction, the generation of exothermic internal heat and the separation of the metal from the slag.

The term silicdn as used herein, is intended to include not only a substantially pure silicon, but also silicon-bearing alloys, such, for example, as ferro-silicon. It has also been found that parts of the silicon may be replaced by equivalent proportions of other metallic reducing agents, such as magnesium, calcium,

etc.

While the preferred embodiment of the process has ,been specificallydescribed, it is to be understood that the limited to its preferred em diment, but may be embodied in other processes, within the scope of-the following claims.

' I claim:

1 The process of making, iron-chromium alloys, which consists in smelting at a temperature attainable in a combustion heated furnace chrome ore and silicon together with hme and fluorspar in sufficlent amounts to render the slag liquid'at temperatures atroc'ess' is not tainable' in a combustion heated/furnace,

a flux-forming mixture containing about 50%-70% by weight of limeof the silicon present and an approximately equal amount. of fiuorspar, substantially as described.v

4,. The process of making iron-chromium alloys, which consists in smelting at a tem-v perature attainable in a combustion heated furnace chrome ore and silicon together with lime and a fluoride in sufficient amounts to render the slag liquid at temperatures attainable in a combustion heated furnace, substantially as described.

5. The process of making iron-chromium alloys, which consists in smelting in a combustion heated furnace chrome ore and silicon together with lime and;,a 'fluoride insufiicient amounts to render theslag liquid at temperatures attainable-in a combustion heated furnace, substantiallyas described.

, 6: The process of makingiron-chromium alloys, which consists in smeltingat a tem perature attainable in a combustion heated furnace chrome ore and silicon together. with lime and fluorspar in suflicient amounts to; render the slag liquid at temperatures attainable in a combustion heated furnace, substantially as described.

l In testimony whereof I have hereunto set my hand.

BYRAMJI n. SAKLATWALLA. 

